The present invention relates generally to cardiology, and, more particularly, to an apparatus and method for reading and analyzing electrocardiographic charts, especially electrocardiographic charts recorded on paper.
Electrocardiograph (EKG) machines are used as a diagnostic tool in medicine, and measure electrical activity in the heart muscle. After each contraction of the heart, an electrical impulse is generated in the sinoatrial node (SA) of the heart. The EKG machine traces the path of the impulse as it spreads though the heart, and produces a graph or trace of the electrical impulses often referred to as an electrocardiogram (ECG). There is a growing need to identify changes that occur in ECGs that are associated with, for example, pharmacological interventions, genotypes and different pathophysiological substrates. For example, one specific need is to determine whether a given compound significantly modulates the repolarization duration process of cardiac beats.
Generally, EKG machines include or are associated with a printing means that produces on paper an ECG chart. Reading and analyzing the paper ECG chart typically requires the use of a ruler or a system of calipers in order to measure and determine certain characteristics of the ECG, such as, for example, time intervals and peak magnitudes. One example of such a caliper system for use in measuring paper ECG charts is described in U.S. Pat. No. 4,388,759, which is herein incorporated by reference. The caliper system described therein is used to determine deflection amplitudes, intervals and frequencies from standard ECG tracings or charts, and consists of two calibrated caliper arms coupled together for rotation about a pivot pin to determine distances between different caliper points. A second example of a caliper system for use in measuring paper ECG charts is described in U.S. Pat. No. 4,936,022, which is also herein incorporated by reference. The caliper system described therein includes a multi-leg caliper device having a plurality of parallel members and pivot points, and is used to measure characteristics of a conventional paper chart ECG by placing several indicia over a suitably calibrated scale and comparing the values on the indicia chart adjacent indicating portions of the multi-leg caliper.
A problem arises when the desired measurement is a time duration between two events. For example, one event may be a peak of one portion of a wave and a valley of another portion. The peak and valley are separated by a substantial vertical distance. An accurate measurement requires projecting the peak and the valley onto the horizontal time axis and then measuring the time between the projected points. The projections must be made to a common horizontal baseline and must be perpendicular thereto. If the baseline is angled from horizontal or if the projection is other than perpendicular, errors in measurement are introduced. Mechanical methods for making such measurements are subject to human and mechanical error.
The above-described and other similar caliper systems are typically restricted to reading only a few of the ECG characteristics of interest. Furthermore, such caliper systems are typically calibrated for use with a paper ECG chart having a predetermined resolution and/or scale, and thus can not be used with other paper charts having a different resolution. Moreover, the caliper-based systems are manual and mechanical in nature, and are thus subject to poor reproducibility and error. Varying resolutions and/or time scales of paper charts and the quality of the ECG tracing on the paper chart are just two examples of factors that have contributed to error and/or poor reproducibility in reading the paper ECG charts. These and other factors which negatively impact the reliability of manually reading paper ECG charts are discussed in greater detail in Savelieva, I., et al., Agreement and Reproducibility of Automatic versus Manual Measurement of QT Interval and QT Dispersion, 81 Am. J. Cardiol. 471-477 (1998), and Murray, A., et al., Errors in Manual Measurement of QT Intervals, 71 Br. Heart J., 386-390 (1994), each of which are incorporated herein by reference.
Therefore, what is needed in the art is a method of reading and analyzing an ECG chart that is less susceptible to error and has a higher reproducibility.
Furthermore, what is needed in the art is a method of reading and analyzing an ECG chart that is less mechanical in nature.
Still further, what is needed in the art is a method of reading and analyzing an ECG chart that is capable of determining a substantial number of the electrocardiogram characteristics of interest.
Moreover, what is needed in the art is a method of reading and analyzing an ECG chart that is adaptable for use with charts having different resolutions and/or scales.
The present invention provides an apparatus and method for analyzing an electrocardiogram (ECG) paper chart.
The invention comprises, in one form thereof, a method of analyzing an electrocardiogram (ECG) paper chart that includes the steps of scanning the ECG chart, to thereby create a computer-readable ECG image file representative of the ECG chart, storing the ECG image file in a memory of a computer, opening the ECG image file and displaying on a computer display an ECG plot corresponding to the ECG image file, calibrating the x-axis and y-axis of the displayed ECG plot with an x-axis scale and a y-axis scale, identifying characteristics of the ECG plot by using an input device connected to the computer, and measuring an axial projection of the identified characteristics by connecting a line at any angle between the two points.
An advantage of the present invention is that reading and analyzing the ECG chart is more automated.
Another advantage of the present invention is that a substantial number of the electrocardiogram characteristics of interest are automatically determined or determined with minimal user input.
Yet another advantage of the present invention is that error and reproducibility in reading and analyzing the ECG chart is reduced.
A still further advantage of the present invention is that it is adaptable for use with ECG charts having different resolutions and/or scales.
Other advantages of the present invention will be obvious to one skilled in the art and/or appear hereinafter.